Frequent Questions

How does precipitation affect radiation levels in the environment?

It is very common for natural background radiation levels to change during precipitation events such as rain, sleet or snow. While there are many more factors that affect radiation levels than just precipitation, radon and radon decay products, which occur naturally may be captured in the precipitation and brought to the ground, causing a temporary increase in radiation levels. However, barometric pressure and the vertical temperature profile, which determine the “lid” under which the radon is generally trapped, may negate the precipitation effect on radiation. Therefore, it is also possible that radiation levels won’t rise during a precipitation event. Snow and sleet may cause radiation levels to decrease since their buildup on the ground may shield radon migration into the atmosphere, as well as shield direct radiation from the ground.

For more information about precipitation sampling analysis and results, visit Envirofacts on EPA.gov.